The publications and other materials used herein to illuminate the background of the invention, and in particular, the cases to provide additional details respecting the practice, are incorporated by reference.
Polysiloxanes, such as poly(dimethylsiloxane) (PDMS), are highly suitable for use as a membrane or a matrix regulating the permeation of drugs in various drug forms, in particular in implants and intra-uterine systems (IUS). Polysiloxanes are physiologically inert, and a wide group of drugs are capable of penetrating polysiloxane membranes, which also have the required mechanical properties.
It is known from the literature that the adding of poly(ethylene oxide) groups, i.e. PEO groups, to a PDMS polymer may increase the perneation of drugs. Publication KL Ullman et al., Journal of Controlled Release 10 (1989) 251-260, describes membranes prepared from a block copolymer which contains PEO and PDMS and the penetration of various steroids through these membranes. It is further known that membranes based on modified PDMS polymers, in which a certain amount of the methyl substituents at the Si-atoms are replaced by trifluoropropyl groups, decrease the permeation of drugs. The publication Ying Sun et al., Journal of Controlled Release, 5 (1987) 69-78, describes the effect on membranes prepared from PDMS, trifluoropropyl substituted PDMS and PDMS/PEO/PMMA (where PMMA is poly(methylmethacrylate)) on the permeation of androgenic and progestenic steroids. The study shows that the permeation for both groups of steroids was lower for the membrane made of trifluoropropyl substituted PDMS than for that made of unmodified PDMS. The publication does not, however, disclose any elastomer made of trifluoropropyl substituted PDMS.